1. Field of the Invention
The present invention relates to a method of manufacturing a magnetic recording medium and a magnetic recording and reproducing device.
Priority is claimed on Japanese Patent Application No. 2010-237570, filed Oct. 22, 2010, the content of which is incorporated herein by reference.
2. Description of the Related Art
Recently, with the remarkable increase of the applicable scope of magnetic recording devices such as magnetic disk devices, flexible disk devices, magnetic tape devices, and the like, their importance has increased, and the remarkable improvement of the recording density of magnetic recording media used in such devices has been sought. In particular, since the introduction of MR heads and PRML technology, an increase in disk surface recording density has increased, and with the recent further introduction of GMR heads, TMR heads, and the like, the increase is continuing at a rate of about 50% per year.
With respect to these magnetic recording media, achievement of higher recording density is required in the future, and in order to achieve this requirement, achievement of high coercivity, high signal-to-noise ratio (SNR), and high resolution of a magnetic layer is necessary. Furthermore, with the recent improvement of line recording densities, there have been efforts to increase the surface recording density by increasing the track density.
In the most up-to-date magnetic recording device, the track density has reached 320 kTPI. However, when the track density is increased, the magnetic recording information between neighboring tracks could interfere with each other, and this causes problems in that a magnetization transition region of their boundary region serves as a noise source, tending to damage the SNR. Since this directly leads to worsening of the bit error rate, it may affect the improvement of the recording density.
Furthermore, in order to increase the surface recording density, it is necessary to further miniaturize the size of respective recording bits on the magnetic recording medium, and to secure a saturation magnetization and magnetic film thickness as large as possible in the respective recording bits. However, when the recording bits are miniaturized, minimum magnetization volume per one bit becomes smaller, and a problem may occur in that recorded data disappears due to magnetization reversal caused by thermal fluctuations.
Furthermore, since the distance between tracks is short, extremely high precision tracking servo technology is required for the magnetic recording device, and, on the other hand, a method of performing a wide range of recording and performing a narrower range of reproduction than the recording in order to eliminate the influence of the neighboring track as much as possible has been generally used. This method has the problem in that although the influence between the tracks can be suppressed to a minimum, it is difficult to sufficiently obtain the reproduction output, and thus it is difficult to secure sufficient SNR.
As a method for solving the above-described problems of heat fluctuations and securing the SNR and the sufficient output, attempts to increase the track density by physically separating the recording tracks from each other by forming of concavo-convexes along the tracks on the surface of the recording medium have been made. Hereinafter, such technology is called a discrete track method, and a magnetic recording medium manufactured by the method is called a discrete track medium.
Furthermore, attempts to manufacture so-called patterned media, in which a data region in the same track is further divided, have been made.
As an example of a discrete track medium, a magnetic recording medium, in which the magnetic recording medium is formed on a nonmagnetic substrate on which a concavo-convex pattern is formed, and a physically separated magnetic recording track and a servo signal pattern are formed thereon, is known (for example, refer to JP-A-2004-164692).
This magnetic recording medium is formed in a manner in which a ferromagnetic layer is formed on the surface of the substrate, on which plural concavo-convexes are formed, through a soft magnetic film, and a protection layer is formed on the surface of the ferromagnetic layer. According to this magnetic recording medium, a magnetic recording region that is physically separated from the surroundings is formed on a convex region.
According to this magnetic recording medium, since the occurrence of magnetic domain walls on the soft magnetic layer can be suppressed, it is difficult for the influence of the heat fluctuations to occur. Furthermore, since there is no interference between neighboring signals, a high-density magnetic recording medium having low noise can be formed.
The discrete track method may be a method of forming a track after forming a magnetic recording medium that is formed of several thin film layers or a method of forming a thin film of a magnetic recording medium after forming a concavo-convex pattern directly on the surface of the substrate in advance or on a thin film layer to form the track (for example, refer to JP-A-2004-178793 and JP-A-2004-178794).
Furthermore, a method of forming a region between magnetic tracks of the discrete track medium with the magnetic characteristic of the region changed by injecting ions of nitride, oxygen, and the like or irradiating a laser onto a pre-formed magnetic layer has been disclosed (refer to JP-A-5-205257, JP-A-2006-209952, and JP-A-2006-309841).
As described above, in manufacturing the so-called discrete track media or patterned media having a magnetically separated magnetic recording pattern, the method of forming the magnetic recording pattern may include (1) the method of forming the magnetic recording pattern by reforming the magnetic characteristic of the magnetic layer through exposing a part of the magnetic layer to reactive plasma using oxygen or halogen or reactive ions, and (2) the method of forming the magnetic recording pattern through processing of a part of the magnetic layer by ion milling and smoothing the surface by filling of a nonmagnetic material in the processed places.
The above-described manufacturing method (1) has the advantages in that since it is not required to physically process the magnetic layer, less dust occurs, and thus it is easy to obtain a clear and smooth surface. However, the manufacturing method (1) has the disadvantages in that the surface of the magnetic layer is oxidized or halogenated. Furthermore, corrosion of the magnetic recording medium (migration of magnetic particles such as cobalt that are included in the magnetic layer) occurs, starting from the oxidized or halogenated region.
Furthermore, the manufacturing method (2) has problems in that since the magnetic layer is processed, dust occurs and the surface of the magnetic recording medium is contaminated. Furthermore, the manufacturing method (2) has problems in that dust is attached to the surface during the processing, and due to this, the smoothness of the surface of the magnetic recording medium is deteriorated. Furthermore, the manufacturing method (2) has problems in that it is required to fill the nonmagnetic material in the processed place of the magnetic layer, and thus the manufacturing process is complex.